Theses and Dissertations

Chapter 1: Functional Specialization and Arm Length in Octopus bimaculoides<br/>Although studies are limited, there is some evidence that octopuses use their arms for specialized functions. For example, in Octopus maya and O. vulgaris, the anterior arms are utilized more frequently for grasping and exploring (Lee, 1992; Byrne et al., 2006a), while posterior arms are more frequently utilized for crawling in O. vulgaris (Levy et al., 2015). In addition, O. vulgaris uses favored arms when retrieving food and making contact with a T-maze as dictated by their lateralized vision (Byrne, 2006b). O. vulgaris also demonstrates a preference for anterior arms when retrieving food from a Y-maze (Gutnick et. al. 2020). In Octopus bimaculoides bending and elongation were more frequent in anterior arms than posterior arms during reaching and grasping tasks, and right arms displayed deformation more frequently than left arms, with the exception of the hectocotylus (R3) in males (Kennedy et. al. 2020). Given these observed functional differences, the goal of this study was to determine if morphological differences exist between different octopus arm identities, coded as L1-L4 and R1-R4. In particular, the relationship between arm length and arm identity was analyzed statistically. The dataset included 111 intact arms from 22 wild-caught specimens of O. bimaculoides (11 male and 11 female). Simple linear regressions and an analysis of covariance were performed to test the relationship between arm length and a number of factors, including body mass, sex, anterior versus posterior location, and left versus the right side. Mass had a significant linear relationship with arm length and a one-way ANOVA demonstrated that arm identity is significantly correlated with arm length. Moreover, an analysis of covariance demonstrated that independent of mass, arm identity has a significant linear relationship with arm length. Despite an overall appearance of bilateral symmetry, arms of different identities do not have statistically equivalent lengths in O. bimaculoides. Furthermore, differences in arm length do not appear to be related to sex, anterior versus posterior location, or left or right side. These results call into question the existing practice of treating all arms as equivalent by either using a single-arm measurement as representative of all eight or calculating an average length and suggest that morphological analyses of specific arm identities may be more informative.<br/><br/>Chapter 2: Predicting and Analyzing Octopus bimaculoides Sensitivity to Global Anesthetic<br/>Although global anesthetic is widely used in human and veterinary medicine the mechanism and impact of global anesthetic is relatively poorly comprehended, even in well-studied mammalian models. Invertebrate anesthetic is even less understood. In order to evaluate factors that impact anesthetic effectiveness analyses were conducted on 22 wild-caught specimens of Octopus bimaculoides during 72 anesthetic events.Three machine learning models: regression tree, random forest, and generalized additive model were utilized to make predictions of the concentration of anesthetic (percent ethanol by volume) from 11 features and to determine feature importance in making those predictions. The fit of each model was analyzed on three criteria: correlation coefficient, mean squared error, and relative error. Feature importance was determined in a model-specific manner. Predictions from the best performing model, random forest, have a .82 correlation coefficient with experimental values. Feature importance suggests that temperature on arrival and cohabitation factors strongly influence predictions for anesthesia concentration. This likely indicates the transportation process was incurring stress on the animals and that cohabitation was also stressful for the typically solitary O. bimaculoides. This long-term stress could lead to a decline in the animal’s well-being and a lower necessary ethanol concentration (Horvath et al., 2013). This analysis provides information to improve the care of octopus in laboratory settings and furthers the understanding of the effects of global anesthetic in invertebrates, particularly one with a distributed nervous system.

Neuromodulation is an emerging field of research that has a proven therapeutic benefit on a number of neurological disorders, including epilepsy and stroke. It is characterized by using exogenous stimulation to modify neural activity. Prior studies have shown the positive effect of non-invasive trigeminal nerve stimulation (TNS) on motor learning. However, few studies have explored the effect of this specific neuromodulatory method on the underlying physiological processes, including heart rate variability (HRV), facial skin temperatures, skin conductance level, and respiratory rate. Here we present preliminary results of the effects of 3kHz supraorbital TNS on HRV using non-linear (Poincaré plot descriptors) and time-domain (SDNN) measures of analysis. Twenty-one (21) healthy adult subjects were randomly assigned to 2 groups: 3kHz Active stimulation (n=11) and Sham (n=10). Participants’ physiological markers were monitored continuously across three blocks: one ten-minute baseline block, one twenty-minute treatment block, and one ten-minute recovery block. TNS targeting the ophthalmic branches of the trigeminal nerve was delivered during the treatment block for twenty minutes in 30 sec. ON/OFF cycles. The active stimulation group exhibited larger values of all Poincaré descriptors and SDNN during blocks two and three, signifying increased HRV and autonomic nervous system activity.

Migration allows animals to track favorable environments and avoid harmful conditions but is energetically costly. There are different types of migration, such as tidal/daily, seasonal, and lifetime. Locust migratory swarms are one such famous phenomena that can have dramatic effects on human livelihoods. During long-distance flight, locusts rely on lipid oxidation from fat stores, while initial flight is fueled by carbohydrates. However, limited studies have tested how dietary macronutrients affect insect flight performance. Therefore, we asked: How do different dietary macronutrient ratios affect prolonged flight migration? We predicted that high carbohydrate diets would lead to high body lipid synthesis which would increase flight performance. We reared locusts in three crowded cages from 5th instar to adulthood on artificial diet varying in p:c ratio, supplemented with lettuce and water tubes, ad libitum. We used 7-14-day old adult males for flight performance assays where each day we used new individuals for tethered flight for 12 h in wind tunnels (~12 km·h-1) and video recorded their flight. We found that locust flight duration and quality increased with a decrease of dietary p:c ratio. Using control groups of locusts, we estimated that across 1 day of flight (up to 12 h), locusts lost on average in all treatments ~25 or ~30% of their total body lipid content. We concluded that long distance flight is improved by a high carbohydrate and low protein diet for L. migratoria by increasing their fuel sources. This work was supported by NSF # 1942054.

Birds naturally have high circulating blood glucose concentrations compared to other vertebrates. Several mechanisms have been proposed to explain their high levels including the lack of an insulin responsive glucose transport protein, higher circulating glucagon concentrations, as well as a reliance on lipid oxidation to fuel the high metabolic demands for flight. We suspected the latter may result in the production of the gluconeogenic precursor, glycerol. Therefore, we examined the hypothesis that gluconeogenesis, via glycerol, contributes to the naturally high glucose concentrations in birds (Madiraju et al., 2014). We captured seven mourning doves, Zenaida macroura, in Tempe, AZ, USA and acclimated the birds to captivity for two weeks. In this crossover design study, doves received either an oral inhibitor of gluconeogenesis (150 or 300 mg/kg metformin) or water (50 ul) each week. We measured blood glucose concentrations using a glucometer at baseline, 30, 60 and 120 minutes following the oral dose. In contrast to mammals and chickens, 300 mg/kg metformin did not alter blood glucose (p>0.05) and 150 mg/kg metformin significantly increased blood glucose concentrations (p=0.043) compared to the oral bolus of water. To examine whether the low dose of metformin stimulated glycogenolysis, thus causing the hyperglycemic effect, we administered the low dose of metformin along with an inhibitor of glycogenolysis, 2.5 mg/kg 1,4-dideoxy-1,4-imino-D-arabinitol (DAB), which prevented the hyperglycemic response (p>0.05 vs. water). These data suggest that low doses of metformin activate glycogenolysis. It is possible that glycogenolysis is also activated at the higher dose, but glycogen may be depleted early on resulting in no measurable changes, given the present study design. In conclusion, and in contrast to the hypothesis, mourning doves may not rely on gluconeogenesis to maintain their naturally high blood glucose concentrations under fed conditions, although further studies with more specific gluconeogenic antagonists and under fasted conditions may be needed to confirm these findings.